1. Field of the Invention
The present invention relates to a mounting device for mounting a power unit on a vehicle body, and, more particularly, to a power plant mounting device which self generates counter vibrations so as to cancel external vibrations applied thereto.
2. Description of Related Art
For mounting a power unit, including an engine, to a body frame of a vehicle, there have: been known mounting devices of the type having two fluid chambers. Such a power unit mounting device includes a power unit fitting member which is connected to a power unit and a base member which is secured to the vehicle body frame. These members are interconnected by means of an elastically deformable connecting member so as to form a chamber, or cavity, for containing and sealing a fluid, such as air or a liquid, therein. This fluid chamber is divided by a partition having an orifice communicating the two fluid chambers, namely, a main fluid chamber and a secondary fluid chamber in which a diaphragm is disposed. In this power unit mounting device, displacement of the fluid through the orifice causes damping of external vibrations applied to the power unit mounting device.
It has also been known to install a secondary diaphragm so as to form a secondary diaphragm chamber in the main chamber. The secondary diaphragm chamber is filled with a fluid or a gas, the pressure of which is regulated as necessary, and the secondary diaphragm is provided with a mass body functioning as a dynamic damper for reducing external vibrations more effectively. Such a power unit mounting device is known from, for instance, Japanese Unexamined Patent Publication No.59-110935.
In the power unit mounting devices of this kind, the mass body may be formed as a vibratory electromagnetic member which generates vibrations by the aid of an electromagnetic actuator so as to cancel external vibrations applied to or experienced by the mounting device. Such a power unit mounting device is known from, for instance, Japanese Utility'Model Publication No.4-39481.
In these power unit mounting devices which generate vibrations having the same amplitude as, but reverse to the phase of external vibrations applied to the mounting device for the cancellation of the applied external vibrations, it is typical to use a vibratory electromagnetic member having a resonance or resonant frequency out of the band of exciting frequencies of vibrations which the vibratory electromagnetic member is excited to generate. This is because, setting of the resonance frequency of the vibratory electromagnetic member to a frequency within the exciting frequency band causes a deterioration of the follow-up ability of excitation control of the vibratory electromagnetic member and makes the excitation control unstable. In addition to this drawback, there is a problem that the power unit mounting device requires a large amount of energy for driving or exciting the vibratory electromagnetic member.